Multi keyword dispatch gen

[ikitommi]

Before

(mg/sample
 [:multi {:dispatch :type}
  ["duck" :map]
  ["boss" :map]])
;({}
; {}
; {}
; {}
; {}
; {}
; {}
; {}
; {}
; {})

After

(mg/sample
 [:multi {:dispatch :type}
  ["duck" :map]
  ["boss" :map]])
;({:type "boss"}
; {:type "boss"}
; {:type "boss"}
; {:type "boss"}
; {:type "boss"}
; {:type "duck"}
; {:type "duck"}
; {:type "duck"}
; {:type "duck"}
; {:type "boss"})

... especially nice with new :multi merging:

(mg/sample
 [:merge
  [:map [:name :string]]
  [:multi {:dispatch :type}
   ["duck" [:map [:speed :int]]]
   ["boss" [:map [:level :int]]]]])
;({:name "", :level 0, :type "boss"}
; {:name "", :speed -1, :type "duck"}
; {:name "", :level -1, :type "boss"}
; {:name "24m", :level -1, :type "boss"}
; {:name "8ou9", :level 4, :type "boss"}
; {:name "o", :speed -3, :type "duck"}
; {:name "", :speed 2, :type "duck"}
; {:name "", :speed -1, :type "duck"}
; {:name "", :level -15, :type "boss"}
; {:name "HWw6", :level 1, :type "boss"})

[frenchy64]

I wonder if there's any advantage to baking this into :multi itself. Perhaps applicable to json schema generation?

(->
  [:multi {:dispatch :type}
   ["a" :map]]
  m/children
  first last)
;=> [:merge :map [:map [:type [:= "a"]]]]

[ikitommi]

Schema forms should not change on schema creation -> children can't be changed. This is a needed property to ensure schemas can be read back as-is from their (serialised) forms.

There should be explicit action like deref, expand or custom helper do merge this. deref is already used for this (e.g. with :merge) but it would mean that merge implementation needs to be moved from malli.util to malli.core making it even bigger and slower to load - and more code on cljs.

I think this is a good baby step, maybe move it later to malli.util - or to core if it makes most sense. Made it private so easy to move later.